The present invention relates to a high-speed CO2 gas welding method, and more particularly it relates to a method for transferring globules at an almost fixed state, without any accompanying short-circuit, at areas whose voltage is made higher than that in a buried arc area, humping area, and fusing area when carrying out high-speed welding whose speed is 5 meters per minute or more.
In a high-speed CO2 gas welding method whose welding speed exceeds 1.5 meters per minute, no spray transfer is brought about as in inert gas arc welding even if the welding current is increased, the size of the globules becomes remarkably large, wherein short-circuit transfer and globular transfer coexist to cause the stability of the arc to be impaired, and a great deal of spatter occurs.
Also, an action of electromagnetic pressure resulting from an electromagnetic force of an arc itself cannot be ignored, and the influence is reflected by the formation of beads, wherein the surface of a molten pool is subjected to the action and is recessed, and a gouging area in which the bottom of the molten pool or its peripheries are exposed is formed. In addition, as the action of the arc pressure is intensified, that is, the current is increased, the gouging area is widened. Finally, a problem occurs in that solidification at the peripheral portions of the molten pool precedes in a state where the gouging area is not sufficiently filled up due to the exposed portion thereof, wherein humping beads accompanying undercuts are brought about.
Conventionally, in order to solve such a problem in high-speed welding, if a buried arc system is employed, in which the arc length is shortened with the welding voltage being further lowered than usual, it was considered that there was an effect of suppressing generation of large-grained spatter, undercuts and/or humping beads.
However, if the above-described buried arc system is employed in areas in which the welding speed exceeds 1.5 meters per minute, another problem occurs in that the arc heat source is buried deep from the surface of a base metal to cause deep penetration. Further, as shown in FIG. 8, the penetration at the welding joint is made deep, and the surface portion thereof is widened to become projection beads, wherein a constricted portion occurs (to be shaped like a mushroom), and no smooth bead penetration and surface shape can be obtained as in MAG welding. Then, notch toughness of the joint portions is caused to remarkably deteriorate.
It is therefore an object of the invention to provide a high-speed CO2 gas welding method that can remarkably reduce spatter and bring about smooth bead penetration and surface shape as in MIG and MAG welding without producing any undercut and humping beads.
In order to solve the above-described problem, in a high-speed CO2 gas welding method whose welding speed exceeds 1.5 meters per minute according to the invention, a welding voltage and a welding current are determined on the basis of an expression P=K1xc3x97Vw, where, with a welding wire feed speed and a welding wire radius used as inputs, a power factor is P(kW), a melting speed of the welding wire is Vw(g/sec), and k1 is a constant.
Also, in a high-speed CO2 gas welding method whose welding speed is more than and including 2 meters per minute and less than and including 2.5 meters per minute according to the invention, a welding voltage is determined in a range from 6.25xe2x89xa6k1xe2x89xa67.41 on the basis of an expression P=K1xc3x97Vw, where, with a welding wire feed speed and a welding wire radius used as inputs, a power factor is P(kW), a melting speed of the welding wire is Vw(g/sec), and k1 is a constant.
Also, a welding voltage is determined on the basis of an expression P=k2xc3x97Vw2+k3xc3x97Vw, where, with a welding wire feed speed and a welding wire radius used as inputs, a power factor is P(kW), a melting speed of the welding wire is Vw(g/sec), and k2 and k3 are constants.
Also, the above-described constants k2 and k3 areas follows; k2=0.898 and k3=4.625.
In addition, it is assumed that the welding is carried out by a welding apparatus including a robot-controlling device.